Air Flow Meter discussion (WAS: "I'm missing something...)

[Will Reeve]

have a look at

http://www.carlton24v.co.uk/efilist/afmvmap.zip

Microsoft excel spreadsheet containg part of a data log between the AFM (a
bosch flap device) and a map sensor on my car. Both signals were 'straight'
from the sensor. I was investigating it for the inlet tract restriction
reduction. You can see the pressure waveform on the MAP trace if you zoom
in!

Will

-----Original Message-----
From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org]On
Behalf Of Bruce
Sent: 17 November 2002 00:25
To: diy_efi at diy-efi.org
Subject: Re: Air Flow Meter discussion (WAS: "I'm missing something...)




Yep, I used to think that too.
Until someone challenged me with his results.
Then I data logged both my MAF and installed a MAP.
It looks to be a tie or the MAF is slightly faster.
The MAF was a processed output and the MAP was raw data.
The thermistor in the new GM MAFs is very small.
Bruce


From: "Kevin _" <kiggly at hotmail.com>
> Unfortunately, in the automotive world, all the aforementioned sensors
> besides the MAP are VERY slow.  From the airflow change to its reported
> measurement, you have a bare minimum of something like 20ms before all the
> corrections are applied.  On the hotwire, the automotive environment
> requires a very durable sensor, so a big-ole thermistor is usually used as
> the hotwire element, which only adds to its latency.  Combine that with
the
> air response time of a turbo system that has 2 cubic feet of plumbing that
> is being compressed from 1:1 to 3:1 and you're in for some very
> non-representative readings during spoolup and after you get off the gas.
> On the other hand, a general MAP sensor reacts in about 1ms.  This is by
far
> the superior way to go for making a drivable EFI setup.  With the airflow
> measuring devices, you'd probably have to wait about 4 engine cycles to be
> able to calculate an accurate airflow input at 9k rpm (13ms/cycle, total
> wild guess of 40ms latency), where with the MAP setup you're able to catch
> it 1 cycle after the transition.  To take care of the latency issue, you
> just have to piss fuel in with throttle transition corrections.
> BTW - I just joined the list earlier today, there seems to be a lot of
good
> stuff here!
> Kevin


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